The invention relates to a method for operating an internal combustion engine especially of a motor vehicle wherein the fuel is injected directly into the combustion chamber in a first operating mode during an induction phase or in a second operating mode during a compression phase and is ignited. In the method, an air/fuel mixture is drawn by suction into the combustion chamber via a tank venting. Likewise, the invention relates to a control apparatus for an internal combustion engine, especially of a motor vehicle, as well as an internal combustion engine especially for a motor vehicle.
A method of this kind, a control apparatus of this kind and an internal combustion engine of this kind are, for example, known in a so-called gasoline direct injection. There, the fuel is injected into the combustion chamber of the engine in a homogeneous operation during the induction phase and in a stratified operation during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine; whereas, the stratified operation is suitable for the idle operation and part-load operation. For example, for a direct-injecting internal combustion engine of this kind, a switchover takes place between the above-mentioned operating modes in dependence upon the requested torque.
In homogeneous operation, an air/fuel mixture can be supplied to the combustion chamber via a tank-venting system. The fuel mass, which is injected directly into the combustion chamber during the induction phase, is homogeneously swirled until the ignition. For this reason, a homogeneous mixture develops in the combustion chamber. The lambda of the air/fuel mixture in the combustion chamber can be controlled (open loop and/or closed loop) via a lambda control to lambda=1.
In this way, an active charcoal filter, which is loaded with fuel, can again be discharged via a tank venting of this kind during homogeneous operation. The fuel, which vaporizes in a fuel tank, can thus be utilized via the tank venting.
In stratified operation, the problem is present that the air/fuel mixture, which is inducted via the tank venting, is too lean because of its low fuel component and therefore cannot be ignited so that uncombusted fuel is outputted to the ambient.
It is an object of the invention to provide a method for operating an internal combustion engine with which a fuel consumption of the least amount is achievable while simultaneously discharging the lowest possible vaporized fuel to the ambient.
This object is achieved in a method of the above-mentioned type in accordance with the invention in that, during a third operating mode, a lean air/fuel mixture is drawn by suction into the combustion chamber via the tank venting and, in addition, fuel is injected into the combustion chamber in the induction phase and in the compression phase. The task is correspondingly solved with a control apparatus and an internal combustion engine of the respective above-mentioned types.
The third operating mode defines a combination of the homogeneous operation and of the stratified operation. The air/fuel mixture, which is inducted via the tank venting and is too lean, is made richer and therefore can be ignited especially because of the injection of fuel during the induction phase. The total air/fuel mixture, which is disposed in the combustion chamber of the engine, can be ignited by the spark plug and combusted.
In this way, the fuel, which vaporizes from the tank, on the one hand, is supplied via tank venting again to the combustion chamber and is there used. On the other hand, it is ensured that even for a lean air/fuel mixture, which is supplied via the tank venting, a combustion takes place in the combustion chamber and therefore no uncombusted fuel is outputted to the ambient.
In an advantageous further embodiment of the invention, the lambda of the air/fuel mixture, which is inducted via the tank venting, is determined. Here, it is advantageous when the lambda is determined in dependence upon the concentration of the air/fuel mixture and/or in dependence upon the inducted air mass.
In a further advantageous embodiment of the invention, the third operating mode is only carried out when the lambda is greater than a pregiven value. With the aid of the pregiven value, it can be distinguished whether the air/fuel mixture, which is inducted via the tank venting, is sufficiently rich and therefore capable of ignition or is too lean and therefore not capable of ignition. In the last case, the third operating mode can then be executed whereas this would otherwise not perforce be required.
In a further advantageous embodiment of the invention, the distribution of the additional fuel to the compression phase and to the induction phase is determined in dependence upon the fuel supplied via the tank venting. In this way, it is possible to adapt the total fuel mass, which is supplied to the combustion chamber, to the torque to be generated by the engine.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an engine, especially of a motor vehicle. A program is stored on the control element which is capable of being run on a computer, especially on a microprocessor, and is suitable for executing the method according to the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method which the program can carry out. Especially an electric storage medium can be used as a control element, for example, a read-only-memory or a flash memory.
Further features, application possibilities and advantages of the invention will become apparent from the following description of embodiments of the invention which are illustrated in the drawing. All described or illustrated features define the subject matter of the invention by themselves or in any desired combination independently of their summary in the patent claims or their dependency as well as independently of their formulation or presentation in the description and/or in the drawing.